We separate many of the basic fragments of classical logic which are used in reverse constructive mathematics. A group of related Kripke and topological models is used to show that various fragments of the Weak Law of the Excluded Middle, the Limited Principle of Omniscience, and Markov’s Principle, including Weak Markov’s Principle, do not imply each other.

[25]Simpson, S., Subsystems of Second Order Arithmetic, Association for Symbolic Logic/Cambridge University Press, Cambridge, 2009.

[26]Toftdal, M., Calibration of ineffective theorems of analysis in a constructive context, Master’s thesis, University of Aarhus, 2004; also as A Calibration of ineffective theorems of analysis in a hierarchy of semi-classical logical principles, ICALP 2004, LNCS 3142, 2004, pp. 1188–1200.